Gas turbine engines are used to power aircraft, watercraft, power generators, and the like. Gas turbine engines typically include a compressor, a combustor, and a turbine. The compressor compresses air drawn into the engine and delivers high pressure air to the combustor. In the combustor, fuel is mixed with the high pressure air and is ignited. Products of the combustion reaction in the combustor are directed into the turbine where work is extracted to drive the compressor and, sometimes, an output shaft. Left-over products of the combustion are exhausted out of the turbine and may provide thrust in some applications.
Gas turbine engines may include a one or more rotating spools which rotate relative to one another. In one example, a gas turbine engine includes a Low Pressure (LP) spool and a High Pressure (HP) spool. The LP spool interconnects the LP turbine and the LP compressor to rotate together. The HP spool interconnects the HP turbine and the HP compressor to rotate together. As a result the LP spool is configured to pass through the HP spool so that the spools may rotate independently of one another.
Flight vehicles powered by gas turbine engines typically use an engine driven generator for aircraft electrical power needs when underway. Turbofan engines typically locate the generator on an accessory gearbox mounted on the exterior of the engine. The gearbox is driven through an integrated towershaft coupled to the HP spool. In another example, a generator may be embedded in the engine. A generator may be embedded on the LP spool or as part of an embedded HP generator/starter.
Embedded generators pose challenges for several reasons. One challenge is that space available below the aerodynamic flowpath limits the physical size and power available from generators. Another challenge is that the operating environments of embedded generators includes high temperatures, presence of oil and oil mist, engine generated vibrations, etc. Still yet another challenge is that embedded generators require revised durability and maintenance philosophies. Another challenge with embedded generators is that access for maintenance and repair may require complete removal of the engine from the aircraft fuselage which can be time intensive and costly.